The vision aims to revitalise the iconic building by introducing a brand new front entrance onto the Flag Market and reinstating the Lancaster Road entrance, creating a “unique link” between the square and the Guild Hall.

A multi-million pound bid to the Heritage Lottery Fund is set to be made, and the investment in library, museum and exhibition spaces across the building is hoped to turn the Harris into a “creative and community hub” and major attraction.

Supporters have described the drastic changes as a “once in a lifetime” opportunity to transform the Harris, but others have raised fears over the alterations to the Grade I listed structure.

In a joint statement Coun Peter Kelly, Preston Council’s cabinet member for culture and leisure, and County Coun Marcus Johnstone, Lancashire County Council’s cabinet member for cultural services, said: “The scale of ambition is clear.

“This is a once in a lifetime opportunity to transform the Harris; it will become a beacon for local people in the 21st century, drawing visitors to a thriving Preston.

“Creativity will be at the core of the re-imagined Harris, everyone will have the opportunity to make, participate and contribute.

“The Harris, and all that is done there, will be led by the people of Preston, Lancashire and the wider region as a whole.

“We can only really do this by thinking big and opening up the Harris in a way that transforms the building and makes it truly accessible to all.

“Of course, as one of Preston’s most important, historic and listed buildings we have to be sensitive to the architecture and history.

“But time and time again, people have been telling us they want to see the Harris open up and talk about the huge success of the Harris Flights a few years ago.

“Now with this major bid for lottery funding we have the chance to be bold and ambitious in a way we’ve never been able to before.

“It’s time to seize the moment and unlock the true potential of the Harris for this and future generations to come.

“With such a big change proposed for the Harris, it’s only natural we seek peoples’ views.

“Over the next few weeks, months and even couple of years we will be improving the plans to take on board people’s ideas, suggestions and the needs of visitors and the community - so that we can truly deliver a new vision for the Harris.

“One that is highly ambitious but keeps the founding values of Edmund Harris’ legacy to Preston and Lancashire at its core.”

But civic expert Aidan Turner-Bishop raised fears over the major changes proposed for the building.

He said: “I don’t agree with knocking a hole to the Flag Market - I think that would severely damage a nationally important building and I doubt it would get permission from Historic England, and I’m sure the Victorian Society would strongly oppose it. “It’s designed on its plinth because it is trying to reflect classical Roman architecture, and that’s why it didn’t have a door onto the Flag Market.”

He said the idea to reopen the Lancaster Road entrance was “sensible”, but said: “The idea of a thoroughfare through the Harris is a bit naive.”

The bid to the HLF must be submitted by the end of November.

If the first stage is successful, the next step is to work up fully-detailed schemes, planning applications and proposals.